1. Field of the Invention
The present invention relates to methods of and apparatus for processing substrates under a reduced pressure, for manufacturing semiconductor devices and the like. Such processing may include reduced-pressure chemical vapor deposition, thermal oxidation, plasma ashing, and plasma cleaning. More particularly, the present invention relates to a method of and apparatus for vacuum treatment suitable for treatment for ashing organic materials such as a photoresist and a residue thereof on a substrate.
2. Description of the Related Art
Hitherto, a known method of vacuum treatment generally comprises the steps of opening a vacuum chamber, loading a substrate on a susceptor in the open vacuum chamber, closing the vacuum chamber, evacuating the interior of the chamber after closing the chamber, heating the substrate, feeding processing gas into the chamber, opening the chamber after completing treatment, and removing the substrate.
A method of performing vacuum treatment for plasma ashing will be described in detail by way of example with reference to FIG. 17.
A substrate W, such as a silicon wafer, 200 mm in diameter and provided with a photoresist pattern, is loaded by its own weight on a susceptor 2 in a chamber 1, which is initially open. The chamber 1 is then closed and substrate W is then heated by heater 3 to a predetermined temperature.
Next, after evacuating the interior of chamber 1 by an evacuating means 6, processing gas, typically oxygen, is fed by a gas feeding means 7 into chamber 1, and a vacuum state therein is maintained.
Microwave energy from a microwave generator (not shown) provided at chamber 1 is fed into chamber 1 and microwave glow discharge occurs, whereby a plasma of the processing gas is generated. The photoresist pattern on substrate W can be stripped by ashing the photoresist pattern by generating ozone and evacuating chamber 1.
After a predetermined treatment time elapses or by monitoring plasma radiation, microwave emission and feed of processing gas are terminated when ashing of the photoresist is complete.
After evacuating the interior of chamber 1 to a predetermined pressure for removing residual processing gas, the pressure in chamber 1 is released to an ambient pressure by ventilation of the interior of chamber 1. Then, chamber 1 is opened and substrate W, on which the photoresist was stripped, is removed.
In the vacuum treatment apparatus described above, a problem arises when larger wafers, such as a 300 mm diameter wafer (so-called "12-inch wafers"), are processed. This problem, however, was not recognized when 200 mm diameter wafers (so-called "8-inch wafers") were processed. The problem is the generation of non-uniform ashing, that is, non-uniform ashing rates.
This fact was discovered by repeated intensive experiments by the inventors of the present invention and is as follows. Warping of the substrate, which occurs when the substrate is loaded on the susceptor, is generated due to a non-uniform temperature profile caused by non-uniform contact between the upper surface of the susceptor and the substrate. In addition, a longer period of time than expected is required for the warping to disappear and for temperatures over the entire substrate to become uniform. Consequently, when treatment throughput is of a high priority, ashing generally must start before a uniform temperature profile on the substrate is obtained, so that non-uniform ashing occurs.
In other words, it is recognized that a rapid and uniform temperature rise of the entire substrate to a predetermined temperature is an important factor for improving throughput and for performing reliable treatment. Moreover, the above factor not only applies to an ashing apparatus, but also broadly applies to vacuum treatment apparatuses described above, such as those for chemical vapor deposition (CVD), which perform treatment under a vacuum.